We have now identified a subpopulation of human thymocytes that is responsive to retinoid treatment during mitogen stimulation. We can now determine whether our previous findings showing variable effects of retinoid treatment with different lymphoid compartments correlate with the lack or presence of the RA-responsive phenotype. Depending upon its presence in other compartments, e.g., PBL, we will enrich for such lymphocytes to test for RA-responsiveness. In all such cases, lymphocyte activation and analysis will be extended to soluble antigens such as PPD, where RA effects have already been demonstrated, and to MLC-CML systems where we can distinguish retinoid activity on cells specifically responding to group I and group II antigens, i.e., cytotoxic and helper cell precursors, respectively. This approach should provide valuable information for better analyzing the immunological aspects of retinoids in antitumor applications. As a result of knowledge gained from our investigations of RA activity on thymus cell subpopulations, we will extend the study of RA effects on the JM T-ALL cell line to include fresh leukemia cells phenotypically corresponding to the normal thymic counterparts already found to be responsive to retinoid treatment. RA-induced changes will be evaluated by reactivity with monoclonal antibodies as well as acquisition of functional capabilities. Our results in an in vitro model involving sensitization to SRBC suggest that retinoids can augment humoral immune responses in humans. The fact that augmentation of PFC induction still occurs when lymphocytes are preincubated with RA before sensitization to SRBC allows for a convenient means of studying intercellular interactions in this model. Thus, we will separate tonsil cells into subpopulations based upon cell type, maturational stages and functional subsets using established techniques (e.g., E, EA, EAu rosetting; monoclonal antibody reactivity followed by "panning" or FACS separation), separately treat the various fractions with RA and recombine them in various combinations for incubation with antigen. This system should allow us to distinguish the selective effects of RA on lymphocyte subpopulations as well as analyze the cellular requirement(s) for RA enhancement.